The present invention relates to a method of detecting a focus in optics associated with an optical pickup.
Optics of the kind described is known as a device for converging light from a laser to a circular information recording medium via an object lens to thereby read information out of the medium or write information thereinto. In such an optical system, the laser beam, whether reading or writing information, has to be properly focused by the object lens to the recording medium.
The above situation requires a method of determining whether a laser beam has been focused by the object lens to the recording medium. Typical of focus detection methods heretofore proposed is the knife edge type method. However, the prior art knife edge type detection method is not always satisfactory due to limited sensitivity of detection achievable therewith.